1. Field of the Invention
The present invention relates to production of hybrid optoelectronic devices which integrate active optoelectronic and passive optical components into novel hybrid optical devices to be used in optoelectronic systems.
2. Discussion of the Background
In customer optoelectronic systems, large bandwidth, polarization insensitive, low loss devices are required for multi-channel broadcasting. Optical component processing based on self-imaging devices such as multimode interference (MMI) devices is an attractive choice for fabrication. Indeed, due to excellent optical properties and ease of fabrication, multimode interference (MMI) devices have already found applications in laser modulators, splitters, switches, and receivers. Production MMI power splinters, as compared with conventional 1×2 waveguide branches, yield devices with smaller dimensions and do not suffer from non-uniformity of output power as a result of sharp edges near the waveguide branches.
From a component viewpoint, a subscriber loop requires massive power splitting for distribution purposes. As needs in the customer loop intensify, ultra small-dimension, large bandwidth, low loss, low reflection and polarization insensitive devices will be required to accomplish a variety of optical processing, such as for example signal splitting. Furthermore, wavelength division multiplexing (WDM) soon will impact nearly all optical network systems. WDM, by itself, requires integration of a number of active and passive optical components including multi-wavelength sources, multiplexers, wavelength add-drop filters and switches. Due to the diverse characteristics of each of these components, integration onto a singular substrate is an imposing problem with conventional fabrication procedures and standard optical glass materials.
Furthermore, the increasing demand for optoelectroninc systems presents a need in long distance free space applications for optoelectronic systems utilizing steerable high power surface emitting lasers. The development of high power diode lasers with integrated steering capability will play a significant role in free space tracking and communication. Here, as with WDM, integration of optical components onto a singular substrate represents a complex problem.
Sol-gel processing, which utilizes low temperature polymerization, has stimulated considerable research. The sol-gel process can be considered as a method for producing glass and ceramic materials from metallorganic precursors by low temperature polymerization reactions. H. K. Schmidt in“Sol-gel and polymer photonic devices,” SPIE Critical Review, vol. CR68, pp. 192–203, 1995 discloses sol gel processing as a tool for making diverse transparent materials with interesting optical or photonic properties.
However, one obstacle for application of sol-gel inorganic materials into optical devices is the limitation imposed by the maximum attainable crack-free sol-gel glass thickness. Glass-on-silicon technology compatible with single mode fiber for 1.55-μm window requires channel waveguides typically greater than 1 μm in thickness. Fabrication of such components based on oxygen-metal-oxygen materials normally demands iterative cycles of deposition, baking at temperatures around 1000° C., and dry etching. Thus, these processes are costly and time consuming.
Introduction of non-volatile organic groupings with a metal backbone has led to interesting materials, such as organically modified silicon and zirconium alkoxides as discussed by H. K. Schmidt, supra, that have substantially reduced the processing demands.
Relaxation in the processing temperature by incorporating organic groupings, used either as a host or a guest, which can modify the inorganic backbone and reduce the connectivity of the sol-gel network allows thicker film deposition and a lowering of the processing temperature compared to sols which do not include the organic groupings. Furthermore, M. A. Farad et al., in Applied Optics vol. 37, pp. 2429–2434, 1998, and in Electronics Letters, vol. 34, pp. 1940–1941, 1998 disclose use of photopolymerizable organic groups, utilizing organic groupings containing unsaturated bonds, C═C double bond in vinyl or methacryl groups, to enables photopolymerization, and thus, the capability to pattern sol-gel glasses using lithographic techniques. In U.S. Pat. No. 6,054,253, M. A. Fardad et al. disclose photo-patternable organically modified silicates doped with modified zirconium and buthoxyaluminoxytriethoxysilane. However, these materials were require rigorous synthesis and patterning procedures, not conducive to optical device integration.
Thus, a number of issues regarding loss inherent from the sol-gel processing have not been resolved which limit the application of sol-gel processing and thus restrict optical device integration, especially between diverse active and passive optical components. These issues include inherent losses in the sol gel glasses at the operating frequency, unintentional losses due to light scatter at sol-gel glass/air interfaces, and improper design of passive optical components.
As a consequence of the complexities of the integration process and the lack of a suitable sol-gel medium, optoelectronic systems coupling light output from photoelectronic devices into power splitters and beam steering elements have not been integrated onto a singular substrate.